Seals Flashcards
1
Q
Seals used between two stationary parts
A
Static
2
Q
Seals used between a moving and stationary part
A
Dynamic
3
Q
Seals that prevent any fluid from leaking from one side of a system to the other
A
Positive
4
Q
Seals which control the amount of leakage
A
Non-positive
5
Q
All static seals are _______ seals
A
positive
6
Q
These are installed at a joint between two stationary surfaces
A
Gaskets
7
Q
List the common gasket and flange arrangements
A
Flat (full) face, raised face (ring), tongue and groove, Spigot and recess
8
Q
This determines the number of bolts required
A
Thickness of joint material (thin flanges require more bolts)
9
Q
What two things are gaskets made from?
A
metals and non metals
10
Q
Inexpensive gasket, seals well against water, oil, and fuel
A
Paper (temp limit 120C/ 230F)
11
Q
Gasket used in low-load applications, can be impregnated with an elastomer
A
Cork (-30 to 150C)
12
Q
Gasket that has excellent mechanical properties and resists water and air
A
Natural Rubber (Upper temp limit 121C/ 250F)
13
Q
Gasket used only for special applications such as high temps and steam turbines
A
Asbestos
14
Q
Type of plastic gasket that resists heat, oil, and oxidation but does not perform well at low temps
A
Acrylic (Upper temp limit 232C / 450F)
15
Q
Type of plastic gasket that is chemically inert, and performs well in extremely low temperatures
A
Teflon (-190 to 250C)
16
Q
Types of gaskets that are harder and used in high pressure and high temp applications
A
Metallic gaskets (can be solid or composite of several materials)
17
Q
The two types of circular gaskets
A
Ring style and Full face
18
Q
Circular and made from synthetic rubber
A
O-rings
19
Q
O-rings made from materials other than synthetic rubber have what?
A
manufacturers markings on them
20
Q
Where are metallic o-rings used
A
extreme conditions of temperature, pressure, or corrosion
21
Q
Shapes of o-rings used in hydraulic systems
A
Multi-lobed, square, rectangular
22
Q
Compound often used in zero or low pressure applications
A
Sealants
23
Q
Types of sealants
A
Non-hardening, hardening (flexible and rigid), tapes
24
Q
Two categories of dynamic seals
A
contact and clearance
25
These seals make contact with the two surfaces to be sealed
Contact
26
These seals seal without touching each other
Clearance
27
Used as a non-positive seal to control leakage between stationary and moving parts
Packing (contact seal)
28
The three categories of packing
Compression, automatic, floating
29
Packing installed in the moving unit is called
inside-packed (cylinder pistons)
30
Packing installed the stationary unit is called
outside-packing (stuffing box)
31
Compression packing is made of these three classes of material
Fabric, metallic, plastic
32
Self lubricating packing is impregnated with this
graphite or teflon
33
This distributes sealing liquid under pressure to the packing
Lantern ring (seal cage)
34
What does 2-L-3-G indicate?
2 rings of packing, lantern ring, 3 rings of packing, gland
35
How should you stagger the ring joints?
90 degrees from each other
36
How far should the gland initially enter the stuffing box?
1/8" to 3/16"
37
How much should you tighten the gland bolts when initially installing?
a sixth of a turn, or one flat till desired leakage is reached
38
This packing uses system pressure to improve it's sealing action
Automatic packing (V-ring, U-ring, O-rings, and cup packing)
39
What is balanced packing?
Seal on both the ID and OD (V-ring and U-ring)
40
What is unbalanced packing?
Seals on one diameter only (Cup packing)
41
V-ring packing is used in sets of how many?
3 or more
42
What must be used with V-ring packing?
internal and external adapter rings
43
How should V-ring packing sets used on double-acting pistons face
away from each other
44
One-piece molded ring with an endless design is meant to be used singly per seat, unlike v-ring packing
U-ring packing (less than 1500psi)
45
Only has one lip and is considered unbalanced
Cup packing
46
An O-ring sits in a groove whose width is generally ___% to ___% of the O-rings cross section
135% to 150%
47
The squeeze of an O-ring is equal to __% of ring diameter
10%
48
What are standard O-rings rated to?
1500psi up to 3000psi using anti-extrusion rings or backup washers
49
What are backup washers often made of?
leather, teflon, or moulded nylon
50
This is a seal that is retained in a groove but not held in a static position. Seal by spring tension
Floating packing (ex. piston rings)
51
Piston rings are what type of seal
non-positive
52
Seal used in low pressure area (2 to 10psi)
Lip seals
53
Materials used for lip seals
felt, leather, synthetic rubber
54
The two types of lip seals
Single lip and double lip
55
Type of ring seal used in high speed applications
Synthetic
56
Non-positive seal which is mounted into a groove in the housing
Ring seals
57
Non-positive seal that expels foreign material away, common on hydraulic and pneumatic cylinders
Wipers
58
Positive seals used when it is vital no atmospheric contaminants reach working parts
Boots and bellows (Boots short bellows long)
59
Positive seal which has a flexible membrane which spans between the stationary and moving parts
Diaphragm seals (flat and rolling)
60
This seal is more effective than any other dynamic seals in preventing leakage
Mechanical seals
61
This feeds the fluid into the product side of mechanical seals
flushing ports
62
This prevents leakage of corrosive or toxic fluids into the atmosphere
Quenching
63
Non-positive clearance seal mounted in s stationary housing. The simplest of seals
Bushings
64
Non-positive clearance seal with a series of concentric or helical grooves in the housing bore
Annulus
65
Non-positive clearance seal with a cupped washer-like flange, assists the sealing of a ring seal
Slinger seal
66
Non-positive clearance seal with a tongue and groove design, uses a maze like path for foreign material to follow
Labyrinth seal
67
This type of packing only seals in one direction
Automatic
68
On centrifugal pumps and compressors roughly __% of the wear on the shafts is on the outermost rings closest to the gland
70%
69
This packing type is very dense and works well in high pressure situations
Braid over braid
70
Graphite ribbon that is wrapped around the shaft to form rings
Radial wound packing
71
How should spiral wound packing be installed?
With the spiral orientated for shaft rotation
72
What psi must the lantern ring receive to keep the pumping medium away from the packing?
approx 10-15psi
73
What is the proper leakage rate for compression packing?
40 to 60 drops per minute
74
Yarn used on rotating or reciprocating shafts and valves where high temperature must be taken into consideration
Carbon Yarn (up to 315C)
75
Yarn with low coefficient of friction, excellent heat conductivity and chemical resistance.
Graphite yarn (up to 1925C)
76
Fibre used in highly corrosive and oxidizing environments
PTFE Fibre (not exceed 260C)
77
Refers to synthetic yarns and binders braided to form compression packing
Plastic packing
78
Type of packing used in the form of foils or ribbons
Metal packing
79
Fibre packing used to pump cold water, brine, or cold oil and can be used in marine applications
Vegetable fibre
80
Shaft runout should not exceed
0.003"
81
This type of gasket is commonly made of stainless steel, used for high-pressure and high temperature applications
Spiral-wound
82
How do you calculate the the correct size of packing?
Subtract diameter of shaft from the OD of the stuffing box and divide by 2
83
Cup packing is often replaced by this packing
U-ring (less maintenance time)
84
The two types of diaphragm seals
Flat and rolling
85
The primary seal in a mechanical seal is a _______ seal
dynamic
86
The secondary seal in a mechanical seal is a ______ seal
static
87
If the product discharge is used to flush it may have to go through this first
Cyclone strainer
88
This braid packing is very flexible and commonly used for reciprocating applications
Square braid
89
This braid packing is strong and resists being deformed or extruded under high pressures
Interlocking braid
90
If the lantern ring is used to keep out harmful abrasives and chemicals it is most likely located where
at the bottom
91
When are mechanical seals prohibited by law
When pump is used for fire safety
92
How are mechanical seals classified
by arrangement and design
93
How many seal points may be on a mechanical seal?
5 seal points
94
This type of mechanical seal the mating faces do not actually come in contact
Gas-lubricated seals (0.0001"-0.0002" gap)
95
In mechanical seals it is common practice to have the seal faces made of what?
Dissimilar metal (to prevent adhesion)
96
This secondary seal is designed to push against a carbon face without breaking the primary seal
PTFE Wedges
97
What are V-rings usually made of?
PTFE
98
This secondary seal is pushed back and forth axially
Pusher seals
99
The most commonly used pushing mechanisms in mechanical seals are
single spring and multiple spring
100
Seal is used in conditions where no available metals can handle the mediums corrosive environment
PTFE Bellows seal
101
Seals made up of a series of metal plates welded together
Welded metal bellow seals
102
What are the two means of providing the drive for the rotating ring
mechanically or by friction
103
These provide a cavity for holding and circulating a cooling or heating fluid near the seal
Gland jackets
104
These are very common inside seals because of their higher seal face loading and less chance for leakage
Unbalanced seals
105
These optimize seal face loading so that increases in hydraulic force are cancelled out
Balanced seals
106
When are stationary seals used
When shaft speeds exceed 4500 ft/min
107
These are often called environmental seals
Tandem mechanical seals
108
Maximum tolerance for an adequate seal is considered this many light bands
3
109
A seal on the bearing housing is called this
external seal
110
A seal attached to the bearing is called this
integral seal
111
A non pusher type seal is referred to as this
bellows
